This invention relates to an automatic gain control circuit.
In recent years, a large variety of integrable automatic gain control circuits (hereinafter referred to as "AGC circuits") have been proposed as the result of development of integrated circuit techniques. The proposed methods of controlling the gain of a transistor circuit include, for example, the method of changing the emitter current of the transistor for conversion of its mutual conductance, the method of applying a negative feedback to the transistor circuit and the method of controlling voltage impressed across the collector and emitter of the transistor. However, any proposed AGC circuit has not been satisfactory and failed to carry out gain control over a fully broad range of an input signal whose voltage level is widely changed, presenting great difficulties in practical application.